1. Field of the Invention
The present invention relates to a light-responsive photocatalyst composition, which is a composite oxide semiconductor containing tungsten, and which can efficiently absorb visible light emitted from the sun and light emitted from interior lamps, such as fluorescent lamps, etc., and to a method of producing the same.
2. Description of the Related Art
A very large amount of solar energy, which is enough to be used for 30 years is by the entire population of the world, is radiated on the earth every day. Therefore, efforts to efficiently use visible light, which accounts for the majority of solar radiation, have attracted considerable attention for a long time.
Meanwhile, environmental problems, which are negative effects caused by the rapid growth of the economy in the 20th century, are becoming more serious day by day. Particularly, various harmful materials, such as waste dyes, phenols, acetaldehydes, and the like, cause many problems. Since such harmful materials threaten people's comfortable lives, it is required to develop technologies for efficiently removing harmful materials as well as preventing them from being generated. Among methods of removing harmful materials, methods of removing harmful materials using a catalyst are well known and semi-permanently used. In particular, methods of decomposing harmful materials using a photocatalyst, in which the harmful materials are removed using only solar light, without using other kinds of energy, have been researched as a method of decomposing harmful materials using clean energy. However, most research has been conducted on photocatalysts using only ultraviolet rays of solar light. Since ultraviolet rays account for only 4% of the total amount of solar radiation, the fact that photocatalysts use only ultraviolet rays represents a very inefficient use of solar light.
A photocatalyst is a material for accelerating an oxidation-reduction reaction between reactants by absorbing light having an energy greater than a band gap energy, forming electrons and holes, dispersing the electrons and holes into the surface photocatalyst particles, and thus allowing the dispersed electrons and holes to participate in the oxidation-reduction reaction therebetween.
As application examples, methods of decomposing organic matter, such as agricultural chemicals, bad-smelling substances, etc., in water or air and methods of self-cleaning the surface of a solid coated with a photocatalyst, using the electrons and holes formed by such a photocatalytic reaction, are proposed, but these methods are mostly conducted using titanium dioxide (TiO2) Since titanium dioxide (TiO2) has a band gap energy of 3.2 eV, it is active only in the radiation of ultraviolet rays having a wavelength of less than 400 nm. For this reason, currently, titanium dioxide (TiO2) is limitedly applied to outdoor lamps or ultraviolet ray lamps.
Therefore, when photocatalysts responsive to visible light, which accounts for 46% of solar light, are developed, they will be able to use solar light at high efficiency, and will be able to be used indoors as well as outdoors because they can respond to light emitted from fluorescent lamps indoors, where solar light is unattainable.
That is, in order to remove harmful materials, photocatalysts using clean and inexhaustible solar light are attracting attention. However, among the photocatalysts, since titanium dioxide (TiO2), which has been known to be the most effective to date, absorbs only the ultraviolet rays, having short wavelengths, of solar light, it is keenly required to develop visible light-responsive photocatalyst compositions that can absorb the visible light in solar radiation.